Local inhibition of hippocampal nitric oxide synthase does not impair place learning in the Morris water escape task in rats

Recent studies have provided evidence that nitric oxide (NO) has a role in certain forms of memory formation. Spatial learning is one of the cognitive abilities that has been found to be impaired after systemic administration of an NO-synthase inhibitor. As the hippocampus has a pivotal role in spat ial orientation, the present study examined the role of hippocampal NO in s patial learning and reversal learning in a Morris task in adult rats. It wa s found that N-omega-nitro-L-arginine infusions into the dorsal hippocampus affected the manner in which the rats were searching the submerged platfor m during training, but did not affect the efficiency to find the spatial lo cation of the escape platform. Hippocampal NO-synthase inhibition did not a ffect the learning of a new platform position in the same water tank (i.e. reversal learning). Moreover, no treatment effects were observed in the pro be trials (i.e. after acquisition and after reversal learning), indicating that the rats treated with N-omega-nitro-L-arginine had learned the spatial location of the platform. These findings were obtained under conditions wh ere the NO synthesis in the dorsal hippocampus was completely inhibited. On the basis of the present data it was concluded that hippocampal NO is not critically involved in place learning in rats.